Cost of equipment = $120,000
Depreciable cost = $90,000
Useful life = 3 years or 30,000 hours of operation
Depreciation per year = Depreciable cost/3 = 90,000/3 = $30,000
Yr 1 depreciation expense = $30,000
Yr 2 depreciation expense = $30,000
Yr 3 depreciation expense = $30,000
Therefore, the correct answer is b.